Earlier in his career, he worked as a congressional aide to U.S. Representative Harold V. Froehlich (R–WI), and served two years as district attorney of Outagamie County, Wisconsin, before his election to the Assembly.

His re-election in 2011 came at a time of intense partisan attention on the Court, following the election of Republican Governor Scott Walker and litigation around his signature law, 2011 Wisconsin Act 10.

[10] In 1981, he opposed removing criminal penalties on sexual activity and cohabitation between unmarried, consulting adults,[12] though he did express a willingness to repeal the jail terms.

[13] He stated that legalizing sex outside of marriage would increase divorce rates, the number of children born outside of wedlock, welfare payments, sexually transmitted diseases, and abortions.

[15] One month later, Governor Thompson appointed Prosser to the Wisconsin Tax Appeals Commission where he conducted hearings and ruled on disputes related to state taxation.

[16] In an unusual move, a bipartisan group of 77 of the 132 state legislators sent a letter to Thompson supporting the appointment, describing Prosser as, "learned, thoughtful, and fiercely defensive of our system of law".

[21] Opponents of the change argued that restricting free online access may result in private vendors selling the information, and may conflict with Wisconsin's open records law.

[27] Prosser later explained he did not file charges because the case was weak; it involved relatively new sexual assault laws that were untested at the time, and he did not think he could win a jury trial.

[40] A review of emails by the Milwaukee Journal Sentinel indicated that "justices on both sides described the court as dysfunctional, and Prosser and others suggested bringing in a third party for help".

[41] Prosser admitted he overreacted, but justified his statements, saying he had been goaded, bullied and abused by two other justices for a long time,[40] and that the fights were caused by liberal members of the court "ganging up" on him and attempting to create a "foul atmosphere".

[43][44][45][46][47] The dispute occurred during a discussion in Bradley's office with four other Justices present, before the court issued its June 13, 2011 split decision to uphold the law limiting collective bargaining rights for most Wisconsin state public employees.

[48] After initially saying he would refrain from comment until a proper investigation was completed,[49] Prosser denied he choked Bradley saying, "claims made to the media will be proven false."

[5] Leaked files obtained by the Guardian revealed that a network of dark money groups spent $3.5 million to pay for TV and radio ads backing the judge during his 2011 campaign.

[51][52] According to these leaked emails "The push was seen as vital, the documents disclose, as a means of retaining the rightwing majority of the court and thereby preserving the anti-union measures introduced by Walker.

'If we lose [Justice Prosser], the Walker agenda is toast,' one ally writes in an email sent around to the governor’s chief of staff and several conservative lobbyists.

[52] Prosser told the Guardian that four years had passed since his re-election before he joined the decision to close the John Doe investigation, over which time any potential conflict of interest had faded.

"Prosser faced JoAnne Kloppenburg, a long-time but little-known Wisconsin assistant attorney general, in both the February 5, 2011, spring primary, and the April 5 run-off election.

"[57][58] In a survey of attorneys conducted by the Milwaukee Bar Association that was published February 2011, Prosser received more votes saying he was "qualified" than any of his opponents; besting Kloppenburg by a margin of 296 to 112.

Kloppenburg supporters attempted to tie Prosser to the policies of Republican governor Scott Walker, and his March 2011 law limiting most of Wisconsin's public employees' collective bargaining rights.

[20][61][62] Both candidates stated their unhappiness regarding the increased partisan aspect of the race,[63][64] with Prosser claiming that if he was defeated, it would mean the end of judicial independence.

[66] The Wausau Daily Herald reversed its primary election endorsement, and urged its readers to vote against Prosser in the general, describing him as "an intemperate figure given to partisan rhetoric".

[67] Citing the earlier statement of Prosser's campaign director that the election is about maintaining a conservative majority on the court, The Capital Times endorsed Kloppenburg.

[68] Prosser was endorsed by the Sun Prairie Star, The Milwaukee Journal-Sentinel, and former Alaska governor Sarah Palin (via Twitter), among others for the general election.

[79] However, Democrats called on Nickolaus to resign, citing her previous employment under Prosser in the mid-1990s as a member of the assembly caucus[76] and questions about her procedures and counts in prior elections.